In processing systems for substrates to be processed such as semiconductor wafers, a substrate transferring apparatus is used for automatic transference or transportation of the semiconductor wafers, between a carrier or a cassette which is a conveying container in which a plurality of semiconductor wafers are supported and a processing section, or between a carrier and a wafer boat which is a processing container. An example of those processing systems using the transferring apparatus is a heat-processing system.
The heat-processing system is used for oxidation, diffusion annealing, film formation or the like of the semiconductor wafers. For example, in the batch-processing type of the heat-processing system, an operation moving semiconductor wafers into the wafer boat from the carrier and loading the wafer boat into the heat-processing furnace and an operation placing back the wafers into the carrier from the unloaded wafer boat are carried out. Thus the loading chamber of the heat-processing system is provided with a substrate transferring apparatus for transferring semiconductor wafers between the carrier and the wafer boat.
FIG. 11 shows a conventional substrate transferring apparatus. The apparatus 80 has a plurality of support plates 9 provided in multi-stairs for supporting and transferring semiconductor wafers W. The plurality of support plates 9 are so provided that they can be raised or lowered, rotated horizontally, and moved forward and backward. Those support plates 9 are inserted into the carrier 6, pick up the semiconductor wafers W on themselves and transfer the semiconductor wafers W from within the carrier 6 into the wafer boat 4 or vice versa.
However, if a semiconductor wafer Wx is projecting out of the cassette or the wafer boat 4 with a positional error such as shown in FIG. 11, the above conventional substrate transferring apparatus can not correct the positional error. In this case, the semiconductor wafer Wx can not be correctly placed on the substrate plate, and the semiconductor wafer Wx may fall out on the way of transferring. An apparatus, which detects a substrate projecting out of a container such as a cassette and gives an alarm has been proposed. However, the above problem is essentially not solved by such proposal.